Process for producing fluorocopolymer

ABSTRACT

A process for preparing a fluorine-containing copolymer by an emulsion polymerization method in the presence of aqueous ammonia as a pH modifier, and a molded article obtainable by melt molding or crosslinking molding the fluorine-containing copolymer. In preparing the fluorine-containing copolymer by coagulation of the fluorine-containing copolymer contained in a fluorine-containing copolymer dispersed aqueous solution, it is preferred to use a cationic surfactant and a water soluble organic solvent as a coagulating agent used for the above coagulation. The surfactant is preferably represented by the, formula (R 4 N + )X −  wherein R is an alkyl group of 1 to 22 carbon atoms, a fluoroalkyl group obtainable by fluorine substituting at least a part of hydrogen atoms present in the above alkyl group or hydrogen, four R&#39;s may be the same or different provided that they are not hydrogen atoms simultaneously, and X is a halogen atom. The process for preparing a fluorine-containing copolymer provides a decrease in a concentration of metal elements, which act as an impurity source, for example, having a metal element concentration of not more than 1 ppm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing afluorine-containing copolymer. More particularly, the present inventionrelates to a process for preparing a fluorine-containing copolymer inwhich the concentration of metal elements, which will be an impuritysource, is lowered.

The present invention further relates to a fluorine-containing copolymerhaving a lowered concentration of metal elements, which will be animpurity source, and suitable, for example, for transportation rolls,sealing materials, hoses, tubes and the like in the field of liquidcrystal and semiconductor production apparatuses, or polymer matrixesfor forming polymer electrolytes of lithium secondary batteries in theelectric field, and also relates to cross-linking (vulcanization) moldedarticles thereof.

2. Description of the Prior Art

Fluorine-containing copolymers generally tend to have enhanced chemicalresistance, heat resistance and higher purity as compared withpolyolefins or the like and have been conventionally used, for example,for molded articles such as transportation rolls, sealing materials,hoses, tubes and the like in the field of liquid crystal andsemiconductor production apparatuses, or polymer matrixes for formingpolymer electrolytes of lithium secondary batteries in the electricfield.

In the liquid crystal and semiconductor production processes, impuritiescontained in the above molded articles formed from thefluorine-containing copolymers such as metal elements and the like arecalled particles and cause wafer surface contamination and therebyinduce product defects. Therefore, the removal of metal elementsremaining is an important subject with the view of improving the yieldof products.

Accordingly, with regard to materials for use in liquid crystal andsemiconductor production apparatuses, it is also desired to usematerials incapable of generating impurity substances, which induceproduct defects.

In polymer electrolytes used for lithium ion secondary batteries, theinclusion of metal elements is undesirable because it is considered thatthe transfer of lithium ion will be interfered or other facts will becaused, to thereby induce a lowering of an ion conductivity of thepolymer electrolyte or to induce a lowering of a discharge capacity inthe cycle of charging and discharging.

Conventionally, fluorine-containing copolymers are prepared in thefollowing manner. A fluorine containing copolymer dispersed aqueoussolution synthesized by an emulsion polymerization method using afluorine-containing anionic surfactant was dropped in an aqueoussolution in which an inorganic salting out agent such as sodium chloridealone, or plural kinds of ones such as sodium chloride, potassium alum,magnesium chloride and the like with stirring and thereby thefluorine-containing copolymer contained therein is aggregated andisolated.

The salting out method, however, has a defect such that as the inorganicsalting out agents used in salting out are contained and adsorbed in thefluorine containing copolymer together with aggregation of the fluorinecontaining copolymer, it is difficult to completely remove the inorganicsalting out agents contained in the fluorine containing copolymer evenif washing thereof with pure water is carried out repeatedly, andfurther fluorine containing copolymers having a high content of metalelements are undesirably prepared due to the inorganic salting out agentused.

As a method for isolating the fluorine containing copolymer withoutusing a salting out agent, there is a freeze-coagulation method ofcarrying out coagulation by freezing a fluorine-containing copolymerdispersed aqueous solution. The fluorine containing copolymer preparedby this method has adsorbed and contained an anionic surfactant and a pHmodifier used in the preparation of the copolymer so that the copolymeris disadvantageous for decreasing impurities and is not preferable inviewpoint of productivity.

As a method of isolating the fluorine containing copolymer without usingthe salting out method, there are a solution polymerization method and asolution suspension polymerization method.

In the case of preparing the fluorine containing copolymer in anelastomer region, it is advantageous to employ the emulsionpolymerization method in view of the reactivity of the fluorinecontaining monomers and batch efficiency thereof.

The present invention solves the problems associated with the prior artby providing a process for preparing a fluorine containing copolymerwhich produces a high purity fluorine containing copolymer having alowered concentration of metal elements from a fluorine containingcopolymer dispersed aqueous solution prepared by an emulsionpolymerization method, preferably an emulsion polymerization methodwithout using metal element containing starting materials.

The present invention further provides a fluorine containing copolymersuitable, for example, for transportation rolls, sealing materials,hoses, tubes and the like in the field of liquid crystal andsemiconductor production apparatuses, or polymer matrixes for formingpolymer electrolytes of lithium secondary batteries in the electricfield, wherein the uses are obtainable by melt molding or vulcanization(cross-linking) molding the fluorine containing copolymer prepared bythe above method and have a lowered concentration of metal elements.

SUMMARY OF THE INVENTION

The process for preparing a fluorine containing copolymer by an emulsionpolymerization method in the presence of a pH modifier according to thepresent invention is characterized by using aqueous ammonia as the pHmodifier.

In the preferred embodiment of the present invention, it is preferred touse a cationic surfactant and a water soluble organic solvent as acoagulating agent in the preparation of the fluorine containingcopolymer by coagulating a fluorine containing copolymer in a fluorinecontaining copolymer dispersed aqueous solution prepared with theemulsion polymerization method.

Furthermore, the cationic surfactant is preferably represented by thefollowing formula:(R₄N⁺)X⁻in the formula, R is any one of an alkyl group of 1 to 22 carbon atoms,a fluoroalkyl group obtainable by fluorine replacement of at least onepart of hydrogen atoms present in the alkyl group, and a hydrogen atom,four R's may be the same or different, provided that four R's are nothydrogen atoms simultaneously, and x is a halogen atom.

The emulsion polymerization is preferably carried out in the presence ofan anionic surfactant as an emulsifying agent.

The fluorine containing copolymer of the present invention is obtainableby the above process and the resulting fluorine containing copolymer hasa metal element concentration of not more than 1 ppm.

The fluorine containing copolymer melt molded article of the presentinvention is obtainable by melt molding the above fluorine containingcopolymer.

The fluorine containing copolymer vulcanization molded article of thepresent invention is obtainable by vulcanization molding the abovefluorine containing copolymer.

According to the process for preparing the fluorine containing copolymeraccording to the present invention, a high purity fluorine containingcopolymer having a lowered metal element concentration is obtainablewith a simple procedure from the fluorine containing copolymer dispersedaqueous solution prepared by the emulsion polymerization method,preferably the emulsion polymerization method without using the metalelement containing raw materials.

The molded articles obtainable by melt molding or vulcanization(cross-linking) molding the fluorine containing copolymer prepared bythe above method have a lowered concentration of metal elements and aresuitable, for example, for transportation rolls, sealing materials,hoses, tubes and the like in the field of liquid crystal andsemiconductor production apparatuses, or polymer matrixes for formingpolymer electrolytes of lithium secondary batteries in the electricfield.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the process for preparing the fluorine containing copolymerwill be described in detail.

Process for Preparing Fluorine Containing Copolymer

In the process for preparing the fluorine containing copolymer accordingto the present invention, the fluorine containing copolymer is preparedwith the emulsion polymerization method in the presence of aqueousammonia as a pH modifier. In the preferred embodiment, the fluorinecontaining copolymer is collected by coagulating the resulting fluorinecontaining copolymer dispersed aqueous solution with a coagulatingagent.

In the preferred embodiment of the present invention, a cationicsurfactant and an aqueous organic solvent are used as the abovecoagulating agent.

Emulsion Polymerization

The process for preparing such a fluorine containing copolymer isdivisionally described below. In the present invention, the fluorinecontaining copolymer is prepared by the emulsion polymerization method.The emulsion polymerization method is carried out using raw materials(for example, fluorine containing vinyl monomers such as vinylidenefluoride, chlorotrifluoroethylene and the like), an emulsifier, aninitiator, water, preferably ion exchange water, aqueous ammonia as a pHmodifier, and optionally a chain transfer agent (for example, methanol,ethanol and isopropanol). Any of these components does not desirablycontain metal elements.

In the present invention, the emulsion polymerization is carried outusing, as a pH modifier, a pH modifier free from metal elements,preferably aqueous ammonia without using a pH modifier containing metalelements (for example, disodium hydrogen phosphate 12-hydrate).Therefore, the present invention has an effect such that the fluorinecontaining copolymer in which the content of any of metal elements islowered can be efficiently prepared by conducting the coagulation asdescribed later. The aqueous ammonia is used in such an amount that thepH of the emulsion polymerization solution as a reaction solution is 5to 8.

As an emulsifying agent, conventionally known anionic surfactants can bewidely used. The anionic surfactants are preferably used in viewpoint ofhaving a large difference in ζ-potential between the anionic surfactantand a cationic surfactant, which is one component in the coagulatingagent as described later. As described above, variously known anionicsurfactants can be used as an emulsifier in the present inventionbecause the cationic surfactants having a ζ-potential opposite to thatof the anionic surfactants may be used in coagulation. From theviewpoint of polymerization, in the case of selecting fluorinesurfactants having a small chain transfer function, the anionic fluorinesurfactants are particularly preferred, because the anionic surfactantshave many kinds and a latex has good stability in polymerization.

Examples of the initiator (polymerization initiator) used herein mayinclude peroxides (for example, inorganic peroxides such as ammoniumperoxodisulfate and the like, and organic peroxides such as dialkylperoxide and the like) and redox type water-soluble initiators. Now, itis desirable to not use peroxides for polymerization initiatorscontaining metal elements (for example, sodium peroxodisulfate,potassium peroxodisulfate and the like) from the viewpoint of preparingthe fluorine containing copolymer in which the metal element content islowered.

Preferable examples of the anionic surfactant used as an emulsifier inthe emulsion polymerization may include anionic surfactants notcontaining metal elements, such as ammonium perfluorooctanate (NH₄⁺[C₇F₁₅COO⁻]), ammonium perfluorononanoate (NH₄ ⁺[C₈F₁₇COO⁻]) andammonium perfluoroheptanoate (NH₄ ⁺[C₆F₁₃COO⁻]).

These emulsifiers may be used in an amount such that the concentrationthereof based on the components in the reaction solution containing theabove components is usually from 0.1 to 20.0% by weight.

The concentration of the fluorine containing copolymer (solid component)prepared by emulsion polymerization in the above conditions in a reactorsuch as an autoclave or the like, in the reaction solution (fluorinecontaining copolymer dispersed aqueous solution), which is notparticularly limited, is about from 5 to 40% by weight.

Coagulation

In the next place, the fluorine containing copolymer dispersed aqueoussolution (reaction solution) is treated with the coagulating agent andthereby the fluorine containing copolymer is coagulated. In thisprocedure, the coagulating agent containing the cationic surfactant andthe water soluble organic solvent is preferably used.

Preferable examples of the cationic surfactants may include those freefrom metal elements, i.e. cationic surfactants represented the followingformula (A):(R₄N⁺)X⁻in the formula (A), R is any one of an alkyl group of 1 to 22 carbonatoms, a fluoroalkyl group obtainable by fluorine replacement of atleast one part of hydrogen atoms present in the alkyl group, and ahydrogen atom, four R's may be the same or different, provided that fourR's are not hydrogen atoms at the same time, and X is a halogen atom oran acetoxy group.

The metal free cationic surfactants represented by the formula (A)further may include:

alkyl ammonium chlorides optionally having a methyl group represented bythe formula (A) wherein X is a halogen, particularly Cl (chlorineatoms), i.e. represented by the formula [I]

in the formula [I], R¹, R², R³ and R⁴ may be the same or different eachother, R¹ shows an alkyl group, preferably a long chain alkyl group of10 to 22 carbon atoms, R², R³ and R⁴ each show hydrogen, an alkyl group,preferably an alkyl group having 1 to 22 carbon atoms, a part or all thehydrogen atoms contained in R¹, R², R³ and R⁴ may be substituted withfluorine, such as monoalkyl monomethyl ammonium chloride, monoalkyldimethyl ammonium chloride, monoalkyl trimethyl ammonium chloride,dialkyl dimethyl ammonium chloride, trialkyl monomethyl ammoniumchloride and tetra-alkyl ammonium chloride, provided that the alkylgroup in these compounds of the formula [I] is the same as R¹;

monoalkylamine acetates optionally having a methyl group represented bythe formula (A) wherein X is an acetoxy group (CH₃COO⁻), i.e.represented by the formula [II]:

in the formula [II], R¹, R², R³ and R⁴ may be the same or different eachother, R¹ shows an alkyl group, preferably a long chain alkyl group of10 to 22 carbon atoms, R², R³ and R⁴ each show hydrogen, an alkyl group,preferably an alkyl group having 1 to 22 carbon atoms, a part or all thehydrogen atoms contained in R¹, R², R³ and R⁴ may be substituted withfluorine, such as monoalkyl amine acetate, monoalkyl dimethyl amineacetate and the like; and

monoalkyl amines wherein the alkyl group has 1 to 22 carbon atoms.

At least one of the alkyl groups in each of the surfactants (compoundsfor surfactants) is preferably a long chain alkyl group having at least10 carbon atoms, more preferably a long chain alkyl group having 10 to18 carbon atoms. In the case the surfactant contains two or more alkylgroups, these alkyl groups may be the same or different each other.

Specific examples of the cationic surfactants may include lauryltrimethyl ammonium chloride, dodecyl trimethyl ammonium chloride,stearyl trimethyl ammonium chloride, distearyl dimethyl ammoniumchloride, monoethanol amide stearate, lauryl amine acetate, stearylamine acetate, and further, perfluoroalkyl-trimethyl-ammonium chlorides([C_(n)F_(2n+1)(CH₃)₃N]^(+.Cl) ⁺ wherein n is an integer of about 1 to22) obtainable by fluorinating these alkyl groups directly bonded to Natom in the above cationic surfactants.

Of these cationic surfactants, those represented by the formula (R₄N⁺)X⁻wherein R is the same in the formula (A), X is a halogen atom,preferably Cl, or an acetoxy group (CH₃COO⁻), more preferably X is Clare preferred because, for example, they are easily available.

These cationic surfactants may be used singly or in combination with twoor more.

If a coagulating agent containing a metal compound, for example, metalsalts (such as calcium chloride, sodium chloride or potassium alum) isused in place of the above cationic surfactant, the content of metalimpurities in the fluorine containing copolymer is increased in spite ofthe coagulation methods such as the freeze coagulation method or thelike referred to in Comparative Examples 1 to 3 as described later.

Examples of the aqueous organic solvent may include:

alcohols particularly aliphatic alcohols of 1 to 10 carbon atoms such asmethanol, ethanol and isopropanol;

amides such as dimethyl formamide and diethyl acetoamide;

ketones such as acetone and the like;

alkylene glycols such as ethylene glycol, triethylene glycol,tetraethylene glycol, dipropylene glycol, 1,2-propane diol, 1,3-propanediol, 1,2-butane diol, 2,3-butane diol, 1,3-butane diol, 1,4-butanediol, 1,2-pentane diol, 1,5-pentane diol, 2,5-hexane diol,3-methy-1,3-butane diol, 2-methyl pentane-2,4-diol, 3-methylpentane-1,3,5-triol, 1,2,3-hexane triol, and glycerin;

polyalkylene glycols such as polyethylene glycol and polypropyleneglycol;

glycerols such as glycerol, diglycerol and triglycerol;

lower alkyl ethers such as ethylene glycol monomethyl ether, ethyleneglycol monoethyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether and diethylene glycol mono-n-butylether; and

thiodiethanol, N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidalydinone.

Of these water soluble organic solvents, alcohols such as methanol,ethanol, isopropanol and the like are preferred, and further, linear orbranched aliphatic alcohols having 1 to 10 carbon atoms, particularlyhaving 1 to 5 carbon atoms, are preferred from the viewpoint ofcompatibility with the above cationic surfactants.

These water-soluble organic solvents may be used singly or incombination with two or more.

In the present invention, as the cationic surfactant contained in thecoagulating agent, the surfactants [I] typified by stearyl trimethylammonium chloride are particularly used, and further the combined usethereof with the above aliphatic alcohol as the water-soluble organicsolvent is preferred because the coagulating properties are good and thecleaning properties are also good.

Although the amount of the cationic surfactant for use depends theconcentration of the anionic surfactant contained in the fluorinecontaining copolymer dispersed water solution, the cationic surfactantis used in an amount of usually from 0.05 to 30.0% by weight, preferably0.1 to 10.0% by weight in the coagulating agent containing the cationicsurfactant and the water-soluble organic solvent, that is, the cationicsurfactant is used in an amount of usually from 0.3 to 40 parts byweight, preferably 0.5 to 30.0 parts by weight based on 100 parts byweight of the water soluble organic solvent because the recovery of thefluorine containing copolymer due to coagulation and the cleaningproperties are good.

When the amount of the cationic surfactant is less than the above range,the anionic surfactant contained in the fluorine containing copolymerdispersed aqueous solution cannot be sufficiently neutralizedelectrically and thereby the fluorine containing copolymer is hardlycoagulated and the recovery of the fluorine containing copolymer tendsto be lowered. When the amount is over the above range,re-emulsification of the fluorine containing copolymer is caused duringthe coagulation and thereby the recovery of the fluorine containingcopolymer is caused during the coagulation and the recovery of thefluorine containing copolymer due to coagulation tends to be lowered.

The coagulating agent containing the cationic surfactant and thewater-soluble organic solvent is preferably used in an amount of usuallyfrom 0.5 to 10 times by weight, preferably 0.5 to 5.0 times by weightbased on the amount of the fluorine containing copolymer dispersedaqueous solution from the viewpoint of the recovery of thefluorine-containing copolymer and the cleaning properties.

The reaction solution containing the coagulated fluorine containingcopolymer is filtered to separate the water phase by a filtration methodsuch as vacuum filtration, centrifugal filtration, pressure filtrationand the like and the fluorine containing copolymer is prepared.

In the present invention, the cleaning and filtration of the fluorinecontaining copolymer with ion exchange water are desirably repeated sothat the separated filtrate has an ion conductivity of not more than 10μS/cm, preferably about 0.2 to 4.0 μS/cm, followed by drying to separate(prepare) a high purity fluorine containing copolymer in which metalelement concentration is markedly decreased.

In the fluorine containing copolymer thus prepared according to thepresent invention, the concentration of metal elements (for example, Na,Mg, Al, K, Ca, Fe, Cu etc) is preferably as low as possible. Theconcentration of any of metal elements such as Na, Mg, Al or the like isusually not more than 2 ppm, particularly desirably not more than 1 ppm.

As described above, an usable method in the process for preparing thefluorine containing copolymer according to the present invention is anemulsion polymerization method, and preferably is an emulsionpolymerization method using components (raw material monomer,emulsifying agent, pH modifier and the like), which do not contain metalelements as much as possible, particularly using aqueous ammonium as apH modifier. Further, in the preparation of the fluorine containingcopolymer by coagulation from the resulting fluorine containingcopolymer dispersed aqueous solution, the high purity fluorinecontaining copolymer having a lowered concentration of each metalelement (for example, not more than 1 ppm) can be prepared with a simplemethod, for example, using the coagulating agent free from metalelements.

Use of the Resulting Fluorine Containing Copolymer

The resulting fluorine containing copolymer thus separated and purifiedis submitted to use as a melt molded article by melt molding or as avulcanization (crosslinking) molded article by vulcanization(crosslinking) molding.

The vulcanization molding of the unvulcanized fluorine containingcopolymer is carried out using, for example, a vulcanizing agent such asorganoperoxides and the like, and a crosslinking assistant(vulcanization assistant) such as polyfunctional monomers and the like.

For example, the referential example 3 described later shows a fluorinecontaining copolymer, which is a unvulcanized fluorine containingcopolymer, obtainable by copolymerizing a vinylidene fluoride [VdF],tetrafluoroethylene [TFE], hexafluoropropylene [HFP], and a brominatedand/or iodinated unsaturated fluorohydrocarbon as a crosslinking sitesuch as 2-bromotetrafluoroethoxy trifluoroethene (FBrVE,Br—C₂F₄O—CF═CF₂).

In crosslinking (vulcanization) of the unvulcanized fluorine containingcopolymer, for example, as shown in Example 3 described later, it isconsidered that the crosslinking is formed in such a manner thatcarbon-carbon double bond sites (CH₂═CH—) in triallyl isocyanate used asthe vulcanization assistant are opened, bromines (Br) present in thecrosslinking sites in the unvulcanized fluorine containing copolymer arepulled out using an organic peroxide such as2,5-dimethyl-2,5-di(tert-butylperoxy) hexane and the like as avulcanizing agent and the plural sites in the copolymer in which Br'sare pulled out are linked to each other using a polyfunctional monomersuch as triallyl isocyanate and the like as a crosslinking assistant(vulcanization assistant), and as a result, desired vulcanization(crosslinking) molded articles are prepared.

The resulting molded articles are suitably used for transportationrolls, sealing materials, hoses, tubes and the like in the field ofliquid crystal and semiconductor production apparatuses, or polymermatrixes for forming polymer electrolytes of lithium secondary batteriesin the electric field, because the content of any of the metal elementscontained in the resulting molded articles is decreased to usually notmore than 2 ppm, particularly not more than 1 ppm.

Using the process for preparing the fluorine containing copolymeraccording to the present invention, a high purity fluorine containingcopolymer in which the concentration of any of various metal elements isremarkably decreased to, for example, not more than 1 ppm, andvulcanization (crosslinking) molded articles of the high purity fluorinecontaining copolymer can be prepared with a simple procedure from afluorine containing copolymer dispersed aqueous solution prepared by anemulsion polymerization method preferably an emulsion polymerizationmethod without using metal element-containing raw materials.

EXAMPLE

The process for preparing the fluorine containing copolymer according tothe present invention will be described in more detail below withreference to as the following examples, but it should be not limited bythe following examples.

Measurement of Metal Content

To 2 g of a fluorine containing copolymer as a specimen, 1 ml ofconcentrated sulfuric acid was added and incinerated with heating at650° C. for 1 hr in an electric furnace.

The ash component obtained was dissolved in a diluted nitric acid (6N)and the determination of each metal was carried out by an ICP emissionspectrometry.

Referential Example 1

To a 100 L volume SUS 316 made autoclave,

1.0 kg (2.3 mol) of perfluoroammonium octanate (anionic surfactant, NH₄⁺[C₇F₁₅COO⁻]),

0.02 kg (ammonia: 0.3 mol) of 25% aqueous ammonia (pH modifier) and

60 kg (3331 mol) of ion exchange water were charged and sufficientlyde-aerated, and then as a chain transfer agent

0.01 kg (0.2 mol) of isopropanol and as initial charging

5 kg (78.1 mol) of vinylidene fluoride [VdF],

0.30 kg (2.6 mol) of chlorotrifluoroethylene [CTFE, ClFC═CF₂] werecharged and heated to 55° C. The inner pressure of the autoclave was 2.5MPa·G.

When the autoclave inside was at the above inner pressure, 0.05 kg (0.2mol) of peroxoammonium disulfate (polymerization initiator) wasintroduced into the system by a metering pump to start polymerizationreaction.

During the polymerization reaction, when the inner pressure of theautoclave was lowered to 2.4 MPa·G, vinylidene fluoride (VdF) wasadditionally fed to return the inner pressure to 2.5 MPa·G and thisprocedure was repeated until the amount of vinylidene fluoride (VdF)separately added was 15 kg (234.2 mol) provided that the amount is a VdFamount in successively introducing VdF, CTFE etc in a predeterminedcomposition into the reaction system, in particular, the amount usedherein is the total amount of VdF amounts successively added.

The other copolymerization monomer (that is CTFE) was also homogeneouslyadded in a composition ratio VdF/CTFE of 97(% by mol)/3(% by mol) inaccordance with the amount of VdF separately added, that is, the monomermixture having a desired composition ratio was appropriately added tothe reaction system and thereby the copolymerization reaction wasadvanced.

After completion of the addition, the reaction mixture was aged untilthe inner pressure was lowered to 0.5 MPa·G to complete thepolymerization.

The aqueous dispersion solution taken out from the autoclave had a solidcomponent concentration, as measured by a measuring method using aninfrared moisture-meter in measuring conditions at 120° C. for 60 min,of 26% by weight. The measuring method referred to the followingexamples.

Referential Example 2

To a 100 L volume SUS 316 made autoclave,

2.1 kg (4.9 mol) of perfluoroammonium nonanoate (anionic surfactant,NH4⁺[C₈F₁₇COO⁻]),

0.04 kg (0.6 mol) of 25% aqueous ammonia and

50 kg (2776 mol) of ion exchange water were charged and sufficientlyde-aerated, and then as a chain transfer agent

0.01 kg (0.3 mol) of methanol and as initial charging

0.8 kg (0.3 mol) of tetrafluoroethylene [TFE],

2.2 kg (8.0 mol) of perfluoro(ethylvinylether) [FEVE] were charged andheated to 80° C. The inner pressure of the autoclave was 0.85 MPa·G.

When the autoclave inside was at the above inner pressure, 0.03 kg (0.1mol) of peroxoammonium disulfate (polymerization initiator) wasintroduced into the system by a metering pump to start polymerizationreaction.

During the polymerization reaction, when the inner pressure of theautoclave was lowered to 0.80 MPa·G, tetrafluoroethylene [TFE] wasadditionally fed to return the inner pressure to 0.85 MPa·G and thisprocedure was repeated until the amount of TFE separately added was 18.5kg (185.0 mol) After completion of the addition, the reaction mixturewas aged until the inner pressure was lowered to 0.40 MPa·G to completethe polymerization.

The aqueous dispersion solution taken out from the autoclave had a solidcomponent concentration of 31% by weight.

Referential Example 3

To a 100 L volume SUS 316 made autoclave,

0.14 kg (0.3 mol) of perfluoroammonium octanoate,

0.02 kg (0.3 mol) of 25% aqueous ammonia,

0.13 kg (0.5 mol) of 2-bromotetrafluoroethoxy trifluoroethene (FBrVE,Br—C₂F₄O—CF═CF₂) and

33 kg (1832 mol) of ion exchange water were charged and sufficientlyde-aerated, and then as a chain transfer agent

0.07 kg (0.2 mol) of 1-bromo-2-iodotetrafluoroethane and as initialcharging

7.5 kg (117 mol) of vinylidene fluoride [VdF],

1.7 kg (17.0 mol) of tetrafluoroethylene [TFE], and

5.5 kg (36.7 mol) of hexafluoropropylene [HFP],

were charged and heated to 50° C. The inner pressure of the autoclavewas 3.4 MPa·G.

Next, 0.02 kg (0.09 mol) of peroxoammonium disulfate was introduced intothe system by a metering pump to start polymerization reaction.

When the inner pressure was lowered to 0.2 MPa·G with proceeding of thepolymerization reaction, the polymerization was completed.

The aqueous dispersion solution taken out from the autoclave had a solidcomponent concentration of 28% by weight.

Referential Example 4

The procedure of Referential Example 3 was repeated except that 0.1 kg(0.3 mol) of disodium hydrogen phosphate 12-hydrate was used in place of0.02 kg (0.3 mol) of 25% aqueous ammonia and thereby afluorine-containing copolymer dispersed aqueous solution was prepared.

The resulting fluorine-containing copolymer dispersed aqueous solutionhad a solid component concentration of 28% by weight.

Examples 1 to 3

In each of Examples 1 to 3, 10 kg of the fluorine-containing copolymerdispersed aqueous solution prepared in each of Referential Examples 1 to3 was dropped to 10 kg of an 1% by weight ethanol solution of stearyltrimethyl ammonium chloride at ordinary temperature (25° C.), underordinary pressure over 1 hr and thereby coagulation of thefluorine-containing copolymer was carried out. As regards to theresulting fluorine-containing copolymer, the concentrations of metalscontained therein were measured.

In the resulting fluorine-containing copolymer, the concentrations ofNa, Mg, Al, K, Ca, Fe, and Cu were less than 1 ppm respectively.

Comparative Example 1

In this example, 10 kg of the fluorine containing copolymer dispersedaqueous solution prepared in Referential Example 1 was dropped to 10 kgof a 10% by weight calcium hydrochloride aqueous solution over 1 hr andthereby coagulation of the fluorine containing copolymer was carriedout. As regards to the resulting fluorine containing copolymer, theconcentrations of metals contained therein were measured.

The resulting fluorine containing copolymer contained Na, Mg, Al, K, Ca,Fe, and Cu. The Ca concentration was 200 ppm and the concentrations ofthe other metals were less than 1 ppm respectively.

The results are inclusively shown in Table 1.

Comparative Example 2

In this example, 10 kg of the fluorine containing copolymer dispersedaqueous solution prepared in Referential Example 2 was dropped to 10 kgof a 10% by weight sodium hydrochloride aqueous solution over 1 hr andthereby coagulation of the fluorine containing copolymer was carriedout. As regards to the resulting fluorine containing copolymer, theconcentrations of metals contained therein were measured.

The resulting fluorine containing copolymer contained Na, Mg, Al, K, Ca,Fe, and Cu. The Na concentration was 50 ppm and the concentrations ofthe other metals were less than 1 ppm respectively.

The results are inclusively shown in Table 1.

Comparative Example 3

In this example, 10 kg of the fluorine containing copolymer dispersedaqueous solution prepared in Referential Example 3 was dropped to 10 kgof a 10% by weight potassium alum aqueous solution over 1 hr and therebycoagulation of the fluorine containing copolymer was carried out. Asregards to the resulting fluorine containing copolymer, theconcentrations of metals contained therein were measured.

The resulting fluorine containing copolymer contained Na, Mg, Al, K, Ca,Fe, and Cu. The Al concentration was 27 ppm,

The K concentration was 10 ppm and the concentrations of the othermetals were less than 1 ppm respectively.

The results are inclusively shown in Table 1.

Comparative Example 4

In this example, 10 kg of the fluorine containing copolymer dispersedaqueous solution prepared in Referential Example 4 was subjected tofreeze coagulation at −25° C. As regards to the resulting fluorinecontaining copolymer, the concentrations of metals contained thereinwere measured.

The resulting fluorine containing copolymer contained Na, Mg, Al, K, Ca,Fe, and Cu. The Na concentration was 10 ppm and the concentrations ofthe other metals were less than 1 ppm respectively.

The results are inclusively shown in Table 1.

Comparative Example 5

In this example, 10 kg of the fluorine containing copolymer dispersedaqueous solution prepared in Referential Example 4 was dropped to 10 kgof an 1% by weight ethanol solution of stearyl trimethyl ammoniumchloride over 1 hr and thereby coagulation of the fluorine containingcopolymer was carried out. As regards to the resulting fluorinecontaining copolymer, the concentrations of metals contained thereinwere measured.

The resulting fluorine containing copolymer contained Na, Mg, Al, K, Ca,Fe and Cu. The Na concentration was 2 ppm and the concentrations of theother metals were less than 1 ppm respectively.

The results are inclusively shown in Table 1.

Example 4 and Comparative Example 6

In each of Example 4 and Comparative Example 6, a fluorine containingelastomer composition prepared by using the fluorine containingcopolymer obtained in each of Example 3 and Comparative Example 3 inaccordance with the compounding order as shown in Table 2 was subjectedto mastication by a 8 inch roll mill and then vulcanized in thevulcanization conditions as shown in table 2 to prepare a vulcanizationmolded article.

As regards to the resulting vulcanization molded article, the metalcontent was measured in accordance with the measuring method asdescribed above. The results obtained are shown in Tables 1 to 2.

As is clear from Tables 1 and 2, of the vulcanization molded articlesobtained above, the vulcanization molded article prepared in Example 4using the fluorine containing copolymer prepared in Example 3 had adecreased concentration of the metal elements as compared with thevulcanization molded article prepared in Comparative Example 6 using thefluorine containing copolymer prepared in Comparative Example 3.Therefore, the vulcanization molded article prepared in Example 4 issuitably used for transportation rolls, sealing materials, hoses, tubesand the like in the field of liquid crystal and semiconductor productionapparatuses, or polymer matrixes for forming polymer electrolytes oflithium secondary batteries in the electric field.

TABLE 1 Metal Kind and Concentration thereof [ppm] Na Mg Al K Ca Fe CuEx. 1 <1 <1 <1 <1 <1 <1 <1 Ex. 2 <1 <1 <1 <1 <1 <1 <1 Ex. 3 <1 <1 <1 <1<1 <1 <1 Ex. 4 <1 <1 <1 <1 <1 <1 <1 Com. Ex. 1 <1 <1 <1 <1 200 <1 <1Com. Ex. 2 50 <1 <1 <1 <1 <1 <1 Com. Ex. 3 <1 <1 27 10 <1 <1 <1 Com. Ex.4 10 <1 <1 <1 <1 <1 <1 Com. Ex. 5 2 <1 <1 <1 <1 <1 <1 Com. Ex. 6 <1 <125 9 <1 <1 <1

TABLE 2 Component: parts by weight Ex. 4 Com. Ex. 6 Fluorine containingcopolymer in 100 — Ex. 3 Fluorine containing copolymer in — 100 Com. Ex.3 Triallyl isocyanate 5.0 5.0 2,5-dimethyl-2,5-di(tert-butyl- 1.0 1.0peroxy)hexane Primary vulcanization conditions 180° C., 6 min. 180° C.,6 min. Secondary vulcanization 200° C., 15 hr. 200° C., 15 hr.conditions

1. A process for preparing a fluorine containing copolymer by anemulsion polymerization method in the presence of a pH modifier whereinthe pH modifier is aqueous ammonia and wherein a coagulating agentcomprising a cationic surfactant and a water soluble organic solvent isused in the preparation of the fluorine containing copolymer bycoagulating a fluorine containing copolymer in a fluorine containingcopolymer dispersed aqueous solution prepared by the emulsionpolymerization method, the said cationic surfactant represented by thefollowing formula:(R₄N⁺)X⁻ wherein R is any one of an alkyl group of 1 to 22 carbon atoms,a fluoroalkyl group and a hydrogen atom, four R's may be the same ordifferent, provided that four R's are not hydrogen atoms simultaneously,and X is a halogen atom.
 2. The process for preparing a fluorinecontaining copolymer according to claim 1 wherein the emulsionpolymerization is carried out in the presence of an anionic surfactantas an emulsifying agent.
 3. The process for preparing a fluorinecontaining copolymer according to claim 1, wherein the amount of thecationic surfactant is 0.3 to 40 parts by weight based on 100 parts byweight of the water soluble organic solvent.
 4. The process forpreparing a fluorine containing copolymer according to claim 1, whereinthe cationic surfactant is an alkyl ammonium chloride represented by theformula [I]:

wherein R¹, R², R³ and R⁴ may be the same or different, R¹ is an alkylgroup, R², R³ and R⁴ are each independently selected from hydrogen, analkyl group, or an alkyl group substituted with fluorine.
 5. The processfor preparing a fluorine containing copolymer according to claim 4,wherein the alkyl ammonium chloride is selected from the groupconsisting of monoalkyl monomethyl ammonium chlorides, monoalkyldimethyl ammonium chlorides, monoalkyl trimethyl ammonium chlorides,dialkyl dimethyl ammonium chlorides, trialkyl monomethyl ammoniumchlorides, tetra-alkyl ammonium chlorides and perfluoroalkyl ammoniumchlorides.
 6. The process for preparing a fluorine containing copolymeraccording to claim 5, wherein the monoalkyl trimethyl ammonium chlorideis selected from the group consisting of lauryl trimethyl ammoniumchloride, dodecyl trimethyl ammonium chloride and stearyl trimethylammonium chloride.
 7. The process for preparing a fluorine containingcopolymer according to claim 5, wherein the dialkyl dimethyl ammoniumchloride is distearyl dimethyl ammonium chloride.